Controlled crystallization and characterization of cordierite glass-ceramics for magnetic memory disk substrate

Glass-ceramics containing cordierite (2MgO-2Al2O3-5SiO2) as a crystal phase based on the glasses in the system MgO-Al2O3-SiO2 were investigated for the application to magnetic disk substrate for higher storage capacity. Parent glasses were prepared with CeO2 addition as a flux and were crystallized by a controlled 2-step heat treatment The maximum nucleation and crystal growth rates were 2.4 × 109/mm3 · hr at 800 °C and 0.3 μm/hr at 915°C respectively. Only α- cordierite was precipitated after heat-treatment. After nucleation at 800 °C for 5 hours prior to crystallization at 915 °C for 1 hour, the resulting crystal volume fraction and crystal size were 17.6% and 0.3 μm, respectively. Heat-treated specimens through the above condition showed the optimum properties for magnetic memory disk substrates as follows.; Bending strength of 192 MPa, Vickers hardness of 642.1 kg/mm2, thermal expansion coefficient of 39 × 10−7/K and surface roughness of 27 A.